The subject matter disclosed herein relates to couplers and, in particular, to an electromagnetic directional coupler having an electrically large coupler.
FIG. 1 shows a top view of an example coupler 100 and is presented to explain the general operation of the embodiments disclosed herein. In the coupler 100 an input signal is coupled from an input line 104 to an output line 106. Both input and output lines 104,106 may be formed of any type of conductive material such as, for example, a wire or metallic trace. The body 102 of the coupler 100 can be formed of a silicon substrate onto which other elements/layers described below are formed over.
The input signal (shown by arrow 112) provided at an input port 110 is partially transmitted along input line 104 to a transmitted port 114. The transmitted signal received at the transmitted port 114 is shown by arrow 116.
A portion of the power received at the input port 110 may be coupled to an output (or coupled) port 120. The output port 120 may be directly connected by a metal connection to the isolated port 118 to form output line 106. In normal naming context, the input port 110 may be called port 1, transmitted port 114 may be called port 2, output port 120 may be called port 3, and isolated port 118 may be called port 4.
The power incident upon input port 110 is partially coupled to output port 120. The ratio of the power at the output port 120 (of signal shown by arrow 122) to the power at the input port 110 is referred to as the coupling ratio. If a lossless condition is assumed, then the signal splitting losses are 3 dB on both termination port 114 and output port 120. That is, the power of input signal 112 is split into two parts with the power at output port 120 and termination port 114 both being one half the power of the input signal. Of course, due to non-ideal impedance matching and dielectric losses the coupling factor may be below (worse than) 3 dB, but nevertheless power (signal) is coupled from input port 110 to the output port 120.
In space-limited locations, couplers may need to be limited in length in the region where coupling is to occur. To that end, in some instances, rather than the configuration shown in FIG. 1, the coupler 100 may take on more complicated shape.